Mexican Americans, a large and growing minority population, have an incidence of hip fracture about 1/2 that of non-Hispanic whites. The reasons for this lower risk are unclear, but lower fracture risks in other ethnic groups, e.g., blacks, have been ascribed to greater bone mass. The bone mass of Mexican Americans and the relationship of bone mass to risk factors has never been examined. We propose to determine the bone mass of the hip and spine, sites of the most clinically important osteoporotic fractures, in a population based sample of 400 Mexican American and non-Hispanic white women. The study population to be examined has been followed since 1979 by the San Antonio Heart Study. Several risk factors for osteoporosis such as obesity, diet, exercise and medication use have been studied prospectively in this population. Additional risk factors for osteoporosis will be assessed by questionnaire and bone mass will be measured by dual photon absorptiometry. These data will be used to identify any differences in-bone mass between Mexican Americans and nonHispanic whites and to assess which risk factors might account for these differences. These data will also be used to develop predictive models relating risk factors to the bone mass of individuals. This information may yield useful information for clinicians and health care planners by indicating if and for whom bone mass measurements add any substantial information about fracture risk above that provided by clinical assessment alone.